Collateral Damage
Damage that is unintended to the intended outcome.
Originating in the U.S. military, who define the term as "Unintentional or incidental injury or damage to persons or objects that would not be lawful military targets in the circumstances ruling at the time. Such damage is not unlawful so long as it is not excessive in light of the overall military advantage anticipated from the attack. (JP 3-60)" (Source) "collateral" comes from medieval Latin collateralis